Oura Ring 4, with two charges. Purchases in January 2026. I love it so much I upgraded to a 5. Great condition! Tech Specifications Sensors Red and infrared LEDs measure blood oxygen levels Green and infrared LEDs alternate to measure heart rate and heart rate variability 24/7 and respiration rate Digital sensor measures temperature trends Accelerometer tracks movement and activity 24/7 Compatibility Oura App is available in English, Finnish, Japanese, German, French, Spanish, Italian, Norwegian, Swedish, Czech, Dutch, and Danish Supports metric and imperial units of measurement Integrates with 40+ apps Available on iOS and Android Weight and Dimensions Width: 7.90mm Thickness: 2.88mm Weight: 3.3 to 5.2 grams (depending on Oura Ring size) Battery Life 5-8 days of battery life** Typically charges in 20-80 minutes, depending on battery level Quality Materials Non-allergenic titanium on inner & outer surfaces Seamless titanium interior Water resistant up to 100m/328 ft Minor scratches from regular wear are normal Connectivity Bluetooth Low Energy Automatic firmware updates via Oura App EMF-safe Supports airplane mode FCC-certified